1. Field of the Invention
The present invention relates to a cooperative multiple-input multiple-output (MIMO) system based on a partial Zadoff-Chu sequence, more particularly to the cooperative MIMO system and a synchronization method thereof capable of improving the synchronization performance effectively based on a partial Zadoff-Chu sequence.
2. Description of Related Art
In the past two decades, orthogonal frequency division multiplexing (OFDM) technology has become the core of different wireless communication systems, and multiple-input multiple-output (MIMO) technology has been proven effective on improving the capacity and performance of the systems. Therefore, the wireless orthogonal frequency division multiplexing system integrated with the MIMO technology is believed to be a mainstream wireless wideband communication system.
MIMO systems can be implemented in a centralized, cooperative or distributed manner, but MIMO systems are limited by hardware and cost, so that the centralized MIMO system having a plurality of antennas installed thereon has lots of limitations. On the other hand, the cooperative MIMO system comes with different transmission delays, and signals from different distributed cooperative nodes will arrive at the receiver at different timing, and have different carrier frequency offsets (CFOs). Therefore, the cooperative MIMO system has a higher level of difficulty to achieve the synchronization.
As disclosed by J.-J. van de Beek, P. Borjesson, M.-L. Boucheret, D. Landstrom, J. Arenas, P. Odling, C. Ostberg, M. Wahlqvist, and S. Wilson in “A time and frequency synchronization scheme for multiuser OFDM,” IEEE J. Sel. Areas Commun., vol. 17, no. 11, pp.
1900-1914, November 1999, a synchronization method uses different subbands to carry the training data of different transmitters, such that the signals transmitted from different transmitters can be separated in frequency domain, and a band-pass filter restores data transmitted from each transmitter. However, this method requires an additional band-pass filter for each user, thus incurring a higher cost of the system.
As disclosed by F. Guo, D. Li, H. Yang, and L. Cai in “A novel timing synchronization method for distributed MIMO-OFDM system,” in Proc. 2006 IEEE Veh. Technol. Conf.—Spring (VTC 2006-Spring), vol. 4, Melbourne, Australia, May 2006, pp. 1933-1936. Different cycle training sequences are provided for different transmitters, and a receiver identifies different cycle training sequences to distinguish signals transmitted from different transmitters. Although each transmitter has a different cycle training sequence, yet this method still will make the receiver to process a mixed training signal in both the time domain and the frequency domain. As the quantity of transmitters increases, the interference among training signals will become increasingly more serious.
Therefore, it is a main subject for the present invention to provide a cooperative orthogonal frequency division multiplexing system with the capability of effectively separating the training sequences of the transmitters in both time domain and frequency domain to enhance the performance of the system synchronization without requiring any band-pass filter.